Recently, as electronic devices have become smaller, there is a need for a high-capacity secondary battery, and particularly, lithium secondary batteries having higher energy densities than nickel⋅cadmium batteries and nickel⋅hydrogen batteries have drawn attention.
As a cathode active material of the lithium secondary battery, a lithium-containing cobalt oxide (LiCoO2) has been mainly used, and in addition to the material, lithium-containing manganese oxides such as LiMnO2 having a layered crystal structure and LiMn2O4 having a spinel crystal structure and a lithium-containing nickel oxide LiNiO2 have also been used.
Meanwhile, the above-described lithium composite transition metal oxide-based cathode active materials are generally prepared by a solid phase synthesis method by synthesizing a composite transition metal hydroxide-based precursor (M(OH)2) and using the synthesized hydroxide-based precursor and a lithium precursor (LiOH, Li2CO3). However, when a cathode active material is prepared using the hydroxide-based precursor, problems such as deterioration in productivity and economic efficiency occur because the production yield is as low as approximately 70%. In addition, hydroxide-based precursors are metastable in the air. Particularly in a Ni-rich system having a high Ni content, a surface reaction locally occurs due to the high reactivity of Ni with moisture, so that it is difficult to store and handle a hydroxide precursor in the air, and for the local surface reaction, it is difficult to optimize the molar ratio in the reaction with lithium, so that a synthesized cathode active material lacks capacity and lifespan characteristics.
Therefore, there is an urgent need for developing a cathode active material having a novel configuration, which is easily stored and may enhance the electrochemical properties of a lithium secondary battery while enhancing the reaction yield to improve the productivity and economic efficiency.